The invention relates generally to a mold for forming horn reflector antennae; and more particularly, relates to a mold for forming conical horn antennae.
A conical horn reflector antenna is generally formed by the right angled intersection of a cone with a cylinder, although other angular relationships may be suitable. The intersection defines the perimeter of an offset paraboloid section with respect to the X and Y orthogonal axis. The parabolic focal length for a right-angled horn reflector is one half the length of the axis of the cone between the apex and the intersection with the offset paraboloid. Thus, the conical horn reflector antenna includes three geometric shapes; a conical horn, a parabolic section and a cylindrical section. Spherical radio-frequency (RF) waves from the conical horn diverge on the parabolic reflector, and are transformed into planar wave fronts, which radiate from the circular projectile aperture at the outer end of the cylindrical section.
The RF performance of the conical horn antenna is critically dependent upon the accuracy in forming the parabolic reflecting surface and the maintenance of the feed source at the exact focal point of the parabolic surface. Performance is also dependent upon the mechanical and electrical contact at the intersecting joints between the various sections of the antenna. Any gaps at such intersections may result in appreciable RF leakage, which may significantly affect the radiation pattern and render the antenna virtually useless. Usually, the antenna is filled with dried pressurized gases and an air tight membraneous window having no effect on the passage of electromagnetic energy is used to enclose the projectile circular aperture of the antenna. If the dried gases within the antenna are dissipated via any air gaps, moist air may enter the antenna and condense into water. An appreciable accumulation of water will substantially degrade performance, and may even cause the antenna to become inoperative.
Generally, the horn reflector antennae are formed by sheet metal fabrication or fiberglas molding. Sheet metal fabrication requires independent formation of each geometric shape with a plurality of metal pieces.
In sheet metal fabrication, optimum tolerances of the various parts, individually and after assembly, are difficult to maintain, and, frequently varied so appreciably from the optimum to cause measurable degradation in the antenna performance. Often, the economics made optimum design tolerances unfeasible. Furthermore, the multiplicity of joints between parts compounded the probability of RF and air leakage problems.
In prior fiberglas constructions, usually the cone part of the antenna was fabricated from one tool and a combined paraboloid and cylindrical part from another tool. In some instances, when optimum performance was not required, only the cone and paraboloid parts were independently formed, and the cylindrical portion was omitted. However, the elimination of the cylindrical portion degrades antenna performance by removing an important shielding element. Although prior fiberglas techniques enabled antenna constructions to be made in multiple sections, significant errors were made in the relationship of the component antenna sections during assembly. Furthermore the joint(s) at the interface of the attached sections was still a source of significant RF and gas leakage.
An example of a multiple section fiberglas antenna construction may be found in U.S. Pat. No. 3,510,873 (Trevisan-1970). In an embodiment disclosed therein, the antenna included a cone unit and a paraboloid-cylindrical unit connected together at a flanged joint. These assembled units were then connected to a feed or receive wave guide arrangements by a "union" or "transitional" element. The union element was bolted at one end to the cone and at the other end to the wave guide. To achieve optimum performance, the focal point of the parabolic reflector must be coincident with the central axis of the wave guide. An error or deviation of the union element from the optimum position, in either the axial or radial direction, will have substantial, if not the greatest single effect on the electrical performance of the antenna. Thus, the Trevisan antenna, although referred to as a two unit construction is actually a three part construction consisting of the paraboloid-cylindrical unit, the cone unit, and the union element unit.
The aforesaid Trevisan patent also refers to a single unit antenna construction. The union element, which is so essential for antenna performance was not considered as an antenna element. Thus, this antenna is actually a two unit antenna, to wit: the paraboloid-cylindrical and cone unit and the union element unit. The subject invention, on the other hand, provides a single-piece antenna having the union element as an integral part thereof, without requiring mechanical connection between the horn and such union element.
As aforestated, the Trevisan Patent refers to a single piece horn-reflector antenna (which does not include the union element), but it is noted that the Trevisan patent does not disclose the means of tooling for fabricating the single-piece antenna. The invention herein discloses positive means for forming a single piece antenna including a union element, and some means enables repeatible fabrication of such single piece antennae.
In prior fiberglas methods, flexible tools or molds were frequently used for forming one or more of the various units of the antenna. Thus, to subsequently remove the tool, it was necessary to distort or bend the tool during its removal from the fiberglas section. Such distortion at times became permanent, and any sections subsequently formed from the same tool, were dimensionally imperfect. Flexible tooling is generally undesirable since it introduces another source for developing dimensional error. The subject invention overcomes this problem by disclosing means for forming a single-piece horn-reflector, antenna, by the use of rigid dimensionally stable tooling, which may be repeatedly reused without effecting mechanical or electrical antenna specifications.
It is therefore, a primary object of this invention to provide a mold to enable horn-reflector antenna to be formed in a single piece.
Another object is to provide a mold to enable accurate and repeatible spatial relationship to be maintained between the horn, and the other geometric sections of the horn-reflector antenna.
Another object is to provide a mold, which enables strict tolerances of antenna dimensions to be maintained and easily repeated in subsequent antennae fabrications with the same mold; and thereby providing substantially identical performance between antennae.
Another object is to provide a mold which is easily assembled prior to forming the antenna and easily diassembled and removed from the antenna after it is fabricated.
Another object is to provide a mold consisting entirely of rigid and dimensionally stable parts.
Another object is to provide a mold to form horn-reflector antenna having one section for forming a paraboloid-cylinder portion of the antenna and two sections for forming the horn portion of the antenna.
Another object is to utilize substantial portions of the same tooling to form various antenna configurations in a single piece.
Still another object is to provide a mold means which enables a "transitional" portion to be formed to the horn portion of the antenna, whereby optimum coupling of the electro-magnetic waves is achieved between the horn and the associated wave guide of the transmitter or receiver system. A related object is to form the transitional portion to couple with a wave-guide and/or coaxial feed or receive system.